The viruses Flashcards
What type of parasite are viruses
Obligate intracellular parasites
Define virion
W virus particle that is extracellular and can move from one cell to another
5 methods of studying viruses
Tissue culture Physical methods - EM, ultracentifugation Serology/immunological methods DNA sequencing Pathology + transmission studies
What viral structure are those that infect prokaryotic cells
Usually have naked capsids
What viral structure are those that infect eukaryotic cells
Most often enveloped
Viral capsid
Formed form
Packed with
Formed form protein sub units
Packed with viral DNA
What do virions have
Molecular receptors that enable recognition and attachment onto host cells
What is the envelope covering the capsid of eukaryotic viruses derived from
The host cell
Large virus
Mimivirus
Baltimore classification
System used to classify viruses based on their manner of mRNA synthesis
How many Baltimore groups are there?
7
What three things do Baltimore classification take into account?
- If viral genome is DNA or RNA
- If viral genome is ss or ds
- If the sense of a ssRNA is positive or negative
Most common Baltimore classification of viruses that infect bacteria and archaea
dsDNA
ssDNA
Most common classification of viruses that infect eukaryotic cells
RNA viruses
Viral genomes - DNA (5 things)
Reactive - Deoxyribose less reactive due to C-H bonds
Alkaline - DNA stable in alkaline
Grooves - DNA has smaller grooves more resistant to enzymatic attack
Double stranded
Mutation rate - lower
(RAG DM)
Viral genomes - RNA (5 things)
Opposite of DNA
RAG DM
But ribose more reactive due to
C-OH bonds
How are viruses phylogenetically analysed
Comparing proteins rather than ribosomal RNA because they don’t have ribosomes
Oldest group of viruses appear to be
dsRNA
Which viruses may have played a role in transition from RNA to DNA world
Retroviruses
Why have some RNA viruses evolved DNA genomes
To protect their genomes from cellular ribonucleases
Viroids
Small single stranded circular RNAs that don’t have a protein coating (like most viruses).